In the 3rd Generation Partnership Project (3GPP) that is a standardization body for mobile communication systems, a job of developing a specification of an Evolved Packet System (EPS) as the next generation mobile communication system, which is disclosed in NPL 1 that follows, is proceeding. As an access system that is connected to the EPS, a Wireless LAN (WLAN) or Worldwide Interoperability for Microwave Access (WiMAX), as well as Long Term Evolution (LTE) has been under study.
Furthermore, in NPL 1, a job of developing a specification of the EPS in a case of performing roaming has been under study as well. In NPL 1, a network of a home mobile operator that is a roaming destination is disclosed as a Visited-Public Land Mobile Network (V-PLMN), and a network of a home mobile operator that does not perform roaming, with which a UE has a contract, is disclosed as Home-Public Land Mobile Network (H-PLMN).
Additionally, in the 3GPP, a recent increase in traffic due to the access of smartphones to the Internet has been under study, and a method in which concentration of traffic in LTE is avoided by performing switching from LTE to other access systems such as a wireless LAN and WiMAX according to a situation on the assumption that the traffic is difficult to process only with LTE has been under study.
In NPL 2, IP Flow Mobility (IFOM) as a technology in which concentration of traffic is avoided using multiple access systems has been under study and has been defined. IFOM is a technology in which distribution of the traffic can be performed by dividing the access system on the basis of flow. At this point, the flow is possible to identify with a transmission source IP address, a transmission destination IP address, a transmission source port number, a transmission destination IP address, and a protocol number (IP 5 is named after these five parameters).
Furthermore, in NPL 1, Multi Access PDN Connectivity (MAPCON) is disclosed as a technology in which the UE makes connections to different access systems at the same time. In MAPCON, different PDN connections to different access systems are established at the same time and thus connections to different access systems are made at the same time. At this point, the PDN connection is an information element in which an association is formed between the UE, the access system, and a Packet Data Network (PDN).
Furthermore, in NPL 2, a method in which Access Network Discovery and Selection Function (ANDSF) is used as a procedure in which the UE switches to the access system is disclosed. The ANDSF is a function of detecting the access system, selecting one access system from among one or multiple detected access systems, and notifying the UE of the selected access system as a policy of the home mobile operator.
The UE that is notified, by the ANDSF, of the access system as an ANDSF policy determines whether or not the access system that is included in the ANDSF policy is applied, and, in a case where the ANDSF policy is applied, switches to that access system by reflecting the UE policy.
Furthermore, in NPL 3, it is disclosed that the UE receives a RAN policy from an LTE access network. In the same manner as in the ANDSF policy, information for selecting one access system from among multiple access systems is included in the RAN policy.